Swift/XRT follow-up observations of three unidentified INTEGRAL sources
ATel #3078; R. Landi, A. Malizia (INAF/IASF Bologna), A. Bazzano, M. Fiocchi (INAF/IASF Rome), A. J. Bird (Univ. Southampton), N. Gehrels (NASA/GSFC), D. N. Burrows (PSU)
on 14 Dec 2010; 17:02 UT
Credential Certification: Raffaella Landi (firstname.lastname@example.org)
Subjects: X-ray, Gamma Ray, Request for Observations
We report the results of X-ray follow-up observations performed with Swift/XRT of three unidentified
INTEGRAL sources listed in the 4th IBIS Survey Catalogue (Bird et al. 2010, ApJS, 186, 1).
There are three sources detected by XRT within the IBIS positional uncertainty
(none of them are detected above 3 keV):
Source #1: it is detected at 4 sigma c.l. (0.3-10 keV) and is located at
R.A.(J2000) = 02h 11m 44.03s and Dec.(J2000) = -44d 07m 00.3s (5.8 arcsec uncertainty).
It has a counterpart in a USNO-A2.0 object (USNO-A2.0 0450_00755064) with magnitudes R ~17.9, and
B ~18.9; no infrared counterpart is found for this object; in NED, it is associated with the
galaxy APMUKS(BJ)B020945.22-442104.8. The X-ray data are described by a power law with photon
index ~1.9 and a 2-10 keV flux of 1.1 x 10-13 erg cm-2 s-1.
Source #2: is detected at 3.1 sigma c.l. (0.3-10 keV) and its position is at
R.A.(J2000) = 02h 11m 20.0s and Dec.(J2000) = -44d 07m 37.5s (6 arcsec uncertainty).
It coincides with a USNO-A2.0 object (USNO-A2.0 0450_00752627) having magnitude R
~17.9, and B ~19.1. The source has no counterpart in the 2MASS catalogue.
From X-ray data we can only infer a 2-10 keV flux of 5.8 x 10-14 erg cm-2
s-1, assuming a power law with photon index 1.8.
Source #3: is detected at 2.4 sigma c.l. (0.3-10 keV) and has coordinates
R.A.(J2000) = 02h 11m 33.4s and Dec.(J2000) = -44d 11m 10.3s (7 arcsec uncertainty).
No counterpart at other wavelengths is found for this object; the 2-10 keV flux is
3.7 x 10-14 erg cm-2 s-1, assuming a power law with photon index 1.8.
All three sources are most likely associated with the galaxy group LCLG-45078 at z = 0.104;
it is not clear at this stage if the IBIS source is the galaxy group or one of its members.
Just at the border of the IBIS error circle, we find an X-ray source
detected at 4.4 sigma c.l. in the 0.3-10 keV energy band (no detection above 3 keV) and
RA(J2000) = 16h 44m 38.1s and Dec(J2000) = +01d 29m 03.5s (6 arcsec uncertainty).
Within the XRT positional uncertainty we find a USNO-B1.0 object (R ~18.5, and B ~20), which is also
reported in the 2MASS catalogue
(J ~16.8, H ~15.9, and K ~15.1). The XRT location is also compatible with a
radio source (NVSS J164437+012903) having a 20 cm flux of 7.2+/-0.5 mJy.
The X-ray spectroscopy provides a 2-10 keV flux of 2.7 x 10-13 erg
cm-2 s-1, assuming a power law with photon index 1.8.
The X-ray/radio detection together with the high location far above the Galactic plane,
suggests that this is an AGN.
Within the IBIS error circle XRT detects one X-ray source (at 3.9 sigma c.l. in the
0.3-10 keV), which is still observed above 3 keV at 3.6 sigma c.l.. It is located at
RA(J2000) = 18h 45m 40.1s and Dec.(J2000) = +02d 42m 07.3s (6 arcsec uncertainty).
The XRT position is compatible with two 2MASS objects having comparable magnitude
J ~16, H ~15, and K ~15. No counterpart is found at other wavelengths.
The X-ray spectroscopy indicates an absorbed power law spectrum
(Gamma = 1.8, NH ~3 x 1023 cm-2) and a 2-10 keV flux of
8.3 x 10-13 erg cm-2 s-1.